Page:Popular Science Monthly Volume 80.djvu/80

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76
THE POPULAR SCIENCE MONTHLY

A FLASH OF LIGHTNING
By Professor FRANCIS E. NIPHER

WASHINGTON UNIVERSITY, ST. LOUIS

IT is customary to classify lightning discharges into at least two classes. This classification is based on the appearance of the flash. One kind of lightning is called forked lightning and the other sheet lightning. There has been some discussion concerning sheet lightning, it being claimed by some that it is merely an illumination due to a discharge which is hidden from view.

The real fact appears to be that both ends of a lightning flash are usually hidden from view within the two clouds. One of these clouds contains falling drops of water which are overcharged with the negative corpuscles which atoms of all kinds of matter contain when in normal condition. The other cloud contains drops which have less than the normal charge. This cloud has always been said to be positively charged.

The writer has sought to obtain photographic evidence of the conditions within these two clouds, at the instant when the discharge

PSM V80 D080 The overcharged cloud with an inflow of negative fluid.png

Fig. 1. The Overcharged Cloud. An inflow of the negative fluid to the main discharge channel, whose end is seen at the middle of the plate.